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Chemistry and Industry of Forest Products ›› 2022, Vol. 42 ›› Issue (2): 93-100.doi: 10.3969/j.issn.0253-2417.2022.02.013

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Analysis of Gel Change of Urea-formaldehyde Resin with Low Molar Ratio

Ji LI, Yifu ZHANG(), Tao XIONG, Xin SUN, Saiqing XIE   

  1. College of Resources, Environment and Materials, Guangxi University, Nanning 530004, China
  • Received:2020-12-19 Online:2022-04-28 Published:2022-05-06
  • Contact: Yifu ZHANG E-mail:zhyf1026@gxu.edu.cn


Using formaldehyde and urea(F and U, molar ratio 1:1) as raw materials, stable urea-formaldehyde resin(UF) with low F/U was synthesized by "alkali-acid-base" method. The effects of storage time, neutral electrolytes(NaCl, MgCl2) and acidic electrolytes(NH4Cl, AlCl3) on UF were investigated. The storage stability, potential stability and aggregation of UF colloidal particles were analyzed by Zeta potentiometer, laser particle size analyzer(LS), scanning electron microscope(SEM-EDS) and field emission transmission electron microscope(FE-TEM), by which the gel rule of UF was revealed. The results showed that the gel of UF not only embodied the colloidal properties, but also had chemical reaction. Both ions and free formaldehyde restricted the stability of UF. The increase of aggregate size led to the gel of UF. The gel time was related to the type of electrolyte. SEM-EDS and Zeta potential tests showed that the higher ionic species content on the surface of colloidal particles might contribute to the electrostatic stability of colloidal particles; neutral electrolytes had limited effect on the stability of colloidal particles, while acidic electrolytes obviously changed the stability of colloidal particles; the acidic conditions provided by acidic electrolytes promoted the reaction between monomers and linear oligomers in the soluble continuous phase, resulting in the formation of larger size aggregates, leading to the advance of gel. The results of FE-TEM and PSD showed that the gel process of UF might be accompanied by the fusion of colloidal particles. Namely, small particles disappear, while large particles grew accordingly, and eventually developed into larger aggregates until the formation of gel with the consumption of oligomers.

Key words: low molar ratio, urea-formaldehyde resin, electrolyte, colloidal particle, gel

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